Proxima Centauri, the closest star to our Sun, lies just 4.24 light-years away — a distance that sounds (0) manageable on a cosmic scale but presents (1) …………………….(MOUNT) obstacles to human travel. Current spacecraft, even the fastest ones, would take tens of thousands of years to cover this gap, far exceeding any (2) ……………………. (REASON) human lifespan. To make the journey within a single generation, very high speeds would be required, but achieving such velocity demands amounts of energy that are currently (3) ……………………. (ACHIEVE). Einstein’s theory of relativity sets an absolute limit: nothing with mass can reach or exceed the speed of light, as the energy needed approaches (4) ……………………. (FINITE). Even theoretical concepts like laser-propelled light sails face formidable engineering challenges, including precise aiming over trillions of kilometres and protecting tiny probes from collisions with interstellar dust. For crewed missions, the problems multiply. Prolonged exposure to cosmic radiation beyond Earth’s magnetic field would cause severe (5) ……………………. (BIOLOGY) damage, genetic mutations, and increased cancer risk. A multi-generational ship might seem like a solution, but it introduces social, psychological, and genetic issues, such as inbreeding risks and cultural drift over centuries. Experts conclude that without (6) ……………………. (REVOLUTION) breakthroughs in physics — perhaps manipulating space-time itself — interstellar travel to even the nearest star remains (7) ……………………. (ATTAIN)for biological humans, confining our species to the Solar System for the (8) ……………………. (FORESEE) future.